Electric submersible pumps may have multiple pump stages, motors, and protector sections stacked in a single ESP string. Each segment in the string may have radial bearings in that section that support a rotating shaft for that segment. The shafts of the various segments in the string are coupled together mechanically, end-to-end, axially. Conventional ESP pumps intended for use in abrasive applications, for example, may have several ARZ (abrasion-resistant zirconia) radial bearings spaced at roughly equal intervals along the longitudinal axis in the stack of stages. For example, the interval may be approximately ten inches. Such ARZ radial bearings may consist of a ceramic sleeve keyed to the rotating pump shaft and a ceramic bushing located in a bearing carrier. These spaced radial bearings are important in maintaining shaft radial location and minimizing pump vibration in abrasive applications where an initial close-fitting radial bearing pair between mating impeller and diffuser hubs becomes significantly worn and provides minimal shaft support.
As shown in FIGS. 1A and 1B, conventional radial bearings 100 for the shaft 102 of a given single ESP section are evenly spaced, at roughly equal intervals “x”, although the equal intervals may be unique for each section. For example, ESP protectors have radial bearings located at approximately equal intervals determined by length of the protector module. Similarly, ESP motors have radial bearings located at approximately equal intervals as determined by length of the rotor sections. Thus, each pump, protector, and motor section has evenly spaced bearings 100 to provide accurate location and alignment of each high-speed shaft 102 for the associated section, and to hold the shaft 102 for that section true, in spite of shaft vibration. However, radial wear of these bearings 100 and subsequent loss of accurate radial location of the shaft 102 is directly related to radial reaction loads on each bearing 100. A significant portion of the radial reaction loads is caused by vibration.